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Discrete Income Tax Expense

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Effective Income Tax Rate Reconciliation, Including Discrete Items, Percent

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Tax Agreement, Indemnification of Ultimate Liability, Percent

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Tax Cuts And Jobs Act of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit)

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Amount of reasonable estimate for tax liability from transition tax on accumulated earnings of controlled foreign corporation deemed repatriated pursuant to Tax Cuts and Jobs Act of 2017 for which accounting for tax effect is incomplete.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Income Taxes - Additional Information (Details) € in Millions, $ in Millions	3 Months Ended				6 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2018 EUR (€)	Jun. 30, 2018 USD ($)	Jun. 30, 2017	Jun. 30, 2018 USD ($)	Jun. 30, 2017	Dec. 31, 2017 USD ($)
Income Tax Disclosure [Abstract]
Effective income tax rate reconciliation, percent					27.00%	28.40%
Effective income tax rate reconciliation, including discrete items, percent			38.10%	21.20%
Discrete income tax expense			$ 21
Tax Cuts And Jobs Act of 2017, incomplete accounting, provisional income tax expense (benefit)					$ 21		$ 272
Tax Cuts and Jobs Act of 2017, incomplete accounting, transition tax			$ 18		18
Charges recorded for AMT credits					$ 3
Alcoa Corporation
Subsequent Event [Line Items]
Tax agreement, indemnification of ultimate liability, percent			49.00%		49.00%
Forecast
Subsequent Event [Line Items]
FIN 48 reserve	$ 38
Forecast \| Alcoa Corporation
Subsequent Event [Line Items]
Tax agreement, indemnification of ultimate liability, percent	49.00%	49.00%
Forecast \| Spain
Subsequent Event [Line Items]
Potential impact to provision for income taxes	$ 59	€ 51